The Most Versatile Rifle Cartridge For Anywhere (Everywhere) In North America Is...

[Mike1234567]

^^^ Head shots!!

 

[Hocka Louis]

.30-06 Ackley Improved

As if the .30-06 wasn't quite as universal as you might want, the .30-06 Ackley is a .308 Magnum! Plus it still shoots regular .30-06 factory rounds in a pinch.

 

[Mike1234567]

^^^ I've heard of the Ackley but I don't know much about it. I do remember they're a bit on the pricey side. You may have a point though... and a new winner. I should have added another factor in the OP... affordability. Yup... I should have set some pretty low prices for new firearms... maybe as little as $300 for a bolt action and $700 for a semi-auto. Yes, sir, that would have helped solidify the '06 as king caliber.

ETA: Hmm... I just did quick price search. It looks like The A.I. is affordable after all but, so far, I've only found bolt and single action rifles. I'll be searching for a semi-auto version later. I gotta run now though.

 

[Onmilo]

Nope, can't do it.
There are too many good cartridges out there to settle on just one.

 

[Art Eatman]

Enough for this thread. FWIW, in the previous dozen threads on this subject, the '06 has been pretty much the consensus selection...